Most digital projector systems (DLP, LCOS) have low intra-frame contrast ratios on the order of 100:1 when imaging a reflective screen. This is mostly due to flare in the optics (lenses), which scatters light and hence reduces contrast. The human visual system is capable of appreciating closer to 10,000:1 intra-frame contrast ratios, so there is vast room for improvement in digital projection technology.
Furthermore, the peak luminance of digital projectors is often limited to undesirably low levels (e.g. 50 cd/m2) since, due to the low contrast ratios, black levels would be raised objectionably if maximum luminance were increased. For example, with a peak luminance of 50 cd/m2 at a contrast ratio of 100:1, the black levels are 0.5 cd/m2. If the projector peak luminance were increased to 500 cd/m2, the black levels would rise to 5 cd/m2, which viewers would perceive as distinctly grey.
Some displays are 3D displays capable of providing separate images for viewing by viewers' left and right eyes. Maintaining brightness in 3D displays is a particular problem since the polarizers, filters and/or shutters used to control which eye can see each image tend to absorb at least some light.
There is a need for projection display systems capable of improved intra-frame contrast. Included in such need is a need for more effective 3D projection display systems.